1) Field of the Invention
The present invention relates to a method for producing 1,1-diarylethanes and, more particularly, to a method for producing 1,1-diarylethanes by the reaction of styrene or derivatives thereof (hereinafter referred to as "styrenes") with an alkylbenzene using as a catalyst an HL type zeolite with a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of at least 4 or a zeolite obtained by ion-exchanging said HL type zeolite with a di- or tri-valent metal ion.
2) Description of the Related Art
Used as electrical insulating oils, solvents for pressure-sensitive paper purposes, etc., 1,1-diarylethanes have heretofore been prepared by the addition reaction at low temperatures of styrene with an alkylbenzene in the presence of a concentrated sulfuric acid catalyst, as known from Japanese Patent Kokai Publication Nos. 50(1975)-4049. A problem of this addition reaction, however, is that it has to perform the reaction at a low temperature of -5.degree. to 0.degree. C. that a cooling medium is needed, and gives to rise an emulsifying phenomenon at neutralizing and water washing steps, which makes the separation of the product difficult. Another problem is that because of using the concentrated sulfuric acid catalyst, a large amount of heavy materials are produced as by-products. Thus, this method is less effective.
It is also known to use Friedel-Crafts catalysts such as aluminium oxide and boron trifluoride for the addition reaction. Incidental to this method, however, are undesired side-reactions such as the polymerization of styrenes, the formation of decomposed products by disproportionation and the occurrence of heavy materials.
In order to eliminate such problems, it has been proposed to prepare diarylalkanes using a solid acid catalyst, as set forth in Japanese Patent Kokai Publication No. 61(1986)-36499. As disclosed there, styrenes are allowed to react with an alkylbenzene at 130.degree.-190.degree. C., using as a catalyst a faujasite type of synthetic zeolite ion-exchanged with a lanthanide type rare earth cation. A problem with this technique, however, is that due to the need of rising the reaction temperature to higher than the boiling point of the alkylbenzenes, the reaction system should be pressurized to keep it in a liquid phase, making the reaction equipment expensively.
Japanese Patent Kokai Publication No. 63(1988)-238028 discloses a method for producing diphenylalkanes, using as a catalyst an H-Y type zeolite exchanged with hydrogen ions in which the SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio is at least 4, or its modification exchanged with lanthanide type rare earth cations. This method is carried out at a reaction temperature of 100.degree.-120.degree. C. At a reaction temperature below 100.degree. C., however, it is not preferable, since the reaction rate is so slow that no sufficiently high conversion and selectivity can be achieved.
As mentioned above, various methods for producing 1,1-diarylethanes have been known in the art. However, the methods using the concentrated sulfuric acid or Friedel-Crafts catalysts can not disolved any problem such as the reaction temperature, by-products, reaction equipment and the like. On the other hand, the method using the solid acid catalyst has to be carried out at a reaction temperature of at least 100.degree. C. and a selectivity in this method is not enough.
It is thus desired to develop a method for producing 1,1-diarylethanes under more mild conditions and with a high selectivity.